Reply by paratrooper34

Garett, the rabbett block plane’s blade is supposed to be just a little proud of the sides of the body. That allows the blade to get snug into the corners of the work. A shoulder plane blade is exactly the same.

The big thing you are looking for here is that the shoulders and the tenon cheeks are at 90 degrees to each other. If they are not, and the error in the angle is more than 90 degrees to the outside of the shoulders, they will not fit tightly.

Personally, I do not use a shoulder plane or rabbet block plane on the shoulders of my work. I use a sharp marking knife to define the shoulder’s edge, then use hand saws to cut them. the last step I do on the shoulders is where I make the money: I use a chisel and pare each shoulder into the tenon to make the shoulders thin at the perimeter. This way, they have to rest tightly up against the other side and close up nicely. Give it a try, it works very well.